Unnamed Turkish officials say his body may have been disposed of in a nearby forest or on farmland.

Mr Khashoggi disappeared after entering the Saudi consulate in Istanbul on 2 October, where Turkish officials allege he was murdered.

Saudi Arabia denies any knowledge of what happened to him.

Samples taken from the Saudi consulate and the consul’s residence during searches this week are being tested for a match with Mr Khashoggi’s DNA.

Separately, US Secretary of State Mike Pompeo strongly denied having listened to an audio recording Turkey says is evidence of Mr Khashoggi’s murder.

“I’ve heard no tape, I’ve seen no transcript,” he said.

Mr Pompeo also strongly criticised ABC News, which had earlier quoted a senior Turkish official as saying that he had been given access to the recording.

“This is wrong to do to the fiancé of Khashoggi,” he added. “This is a very serious matter that we’re working diligently on, and so to put out headlines that are factually false does no one any good.”

Turkey has previously said it has audio and video evidence of Mr Khashoggi’s murder, but these have not been made public.

The incident has caused considerable strain between Riyadh and its Western allies, with US Treasury Secretary Steven Mnuchin and UK International Trade Secretary Liam Fox becoming the latest senior figures to pull out of a major investment conference in Riyadh next week.

The summit is being hosted by Saudi Crown Prince Mohamed bin Salman to promote his reform agenda.

Media captionUS Secretary of State Mike Pompeo says the Saudis will respond in a “timely fashion”

However, Saudi Arabia says reports on Mr Khashoggi’s death are “completely false and baseless” and that it is “open to co-operation” to find out what happened.

Several high-profile human rights groups have demanded that Turkey ask the UN to investigate the possible killing of Mr Khashoggi.

On Wednesday and Thursday, Turkish investigators spent almost nine hours searching the Saudi consul’s residence, before moving on to the consulate itself about 200m (650ft) away, according to Reuters news agency.

Several vehicles with Saudi diplomatic number plates were filmed by CCTV cameras moving from the consulate to the residence just under two hours after Mr Khashoggi entered the consulate.

How have other countries reacted?

Saudi Arabia is a key ally to many Western countries, especially the US. As one of the world’s biggest oil exporters, it has significant influence on the world stage.

The Dutch and French finance ministers, and the head of the International Monetary Fund, are amongst those now boycotting the summit.